Rotary-Wing Aircraft Torque Coupling with Pad Bearings

ABSTRACT

A torque coupling for a rotor head of a rotary-wing aircraft is configured for rotation with a mast and for causing rotation of an attached yoke. The coupling has trunnions that rotate with the mast and extend generally radially. Pad-bearing assemblies each have a central member coupled to one of the trunnions with a laminated spherical bearing and have laminated pad bearings affixed to opposing sides of the central member. The laminated bearings have alternating rigid and elastomeric layers. A bearing mount is affixed to each pad bearing and is connected to a yoke for rotating the yoke with the mast. The pad-bearing assemblies allow for relative motion between each central member and the associated trunnion and between each central member and the bearing mounts through elastic shear deformation, and this allows for gimballing of the attached yoke relative to the mast.

TECHNICAL FIELD

The present invention relates generally to torque couplings and relatesparticularly to torque couplings used in rotor heads of rotary-wingaircraft.

DESCRIPTION OF THE PRIOR ART

Rotor heads of rotary-wing aircraft, such as helicopters and tiltrotors,are rotated using a rotor mast. The rotor head typically consists of ayoke, torque coupling means for transferring torque from the mast to theyoke, and a plurality of blades attached to the yoke. The blades areoften variable pitch blades, and various configurations of controlmechanisms, which rotate with the rotor head, are used to control theblade pitch.

With many types of control mechanisms, the rotating controls need asmuch space as possible to achieve the most favorable control-systemcoupling terms. Because the rotating control system and the torquecoupling means compete for space in the available volume, engineers mustbalance the desire for small size of the coupling means with the needfor strength, which typically means larger components.

Although great strides have been made in the art of rotor heads,significant shortcomings remain.

SUMMARY OF THE INVENTION

There is a need for an improved torque coupling that provides for areduced size and increased strength for transferring high torque.

Therefore, it is an object of the present invention to provide for areduced size and increased strength for transferring high torque.

A torque coupling for a rotor head of a rotary-wing aircraft isconfigured for rotation with a mast and for causing rotation of anattached yoke. The coupling has trunnions that rotate with the mast andextend generally radially. Pad-bearing assemblies each have a centralmember coupled to one of the trunnions with a laminated sphericalbearing and have laminated pad bearings affixed to opposing sides of thecentral member. The laminated bearings have alternating rigid andelastomeric layers. A bearing mount is affixed to each pad bearing andis connected to a yoke for rotating the yoke with the mast. Thepad-bearing assemblies allow for relative motion between each centralmember and the associated trunnion and between each central member andthe bearing mounts through elastic shear deformation of the elastomericlayers of the pad bearings, and this allows for gimballing of theattached yoke relative to the mast.

The present invention provides for several advantages, including: (1)reduced size; (2) reduced weight; and (3) the ability to transfer hightorque.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, includingits features and advantages, reference is now made to the detaileddescription of the invention taken in conjunction with the accompanyingdrawings in which:

FIG. 1 is an oblique view of a rotor head incorporating a torquecoupling according to a preferred embodiment of the present invention;

FIG. 2 is a partially exploded oblique view of the rotor head of FIG. 1;

FIG. 3 is a partially exploded oblique view of the rotor head of FIG. 1;

FIG. 4 is a side view of a pad bearing of the invention;

FIG. 5 is a is a cross-sectional top view of the pad bearing of FIG. 4along the section line V-V;

FIG. 6 is an oblique view of a rotor head incorporating an alternativeembodiment of the torque coupling of the present invention; and

FIG. 7 is a partially exploded oblique view of the rotor head of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a high-torque coupling suitable for usein a rotor head of a tiltrotor aircraft, which is capable of verticalflight in a helicopter mode and forward flight in an airplane mode. Thecoupling of the invention provides for transmission of higher torquefrom a rotating mast to a rotor yoke while providing for relative motionof yoke at the required angles. The coupling of the invention is morecompact than competing designs, allowing for favorable blade controlsystem coupling terms and allowing for increased airspeed in airplanemode due to increased stability.

In the preferred embodiment, the torque coupling of the presentinvention uses laminated pad bearings and laminated spherical bearingsto allow for the required rotational motion of the yoke relative to themast. The pad bearings have a focus at the center of flapping andpreferably have a chevron-shaped cross-section to improve the stabilityof the pad bearing, though other cross-sectional shapes can be used.Focusing the rigid layers of the pad bearing at the flapping axisgreatly reduces the cocking motion in the spherical bearings. Theimproved design also reorients the spherical cocking to be concentric toa drive trunnion. These improvements allow this coupling to transmit therequired torque while reducing the shear strains in the elastomericcomponents.

Referring to the figures, FIG. 1 through 3 show a rotor head 11 for atiltrotor aircraft, rotor head 11 incorporating a torque coupling 13according to the present invention. Rotor head 11 comprises coupling 13and a yoke 15 mounted to coupling 13 for rotation with coupling 13. Yoke15 is configured to allow for rotor blades (not shown) to be attached toouter portions 17 of yoke 15. Rotor head 11 is shown assembled onto arotor mast 19 for rotation of rotor head 11 when mast 19 is rotatedabout axis 20.

FIGS. 2 and 3 are views of rotor head 11 with coupling 13 shownpartially exploded. Torque is transferred though a splined connectionfrom mast 19 into trunnion carrier 21, which is preferably a unitarypiece having four trunnions 23 extending radially from trunnion carrier21. Torque is transferred from each trunnion 23 into one of a pluralityof pad-bearing assemblies 25. The embodiment shown in FIGS. 1 through 3comprises four pad-bearing assemblies 25, though rotor head 11 can beconfigured to have more or fewer assemblies 25. Each pair of opposingtrunnions 23 forms a flapping axis 26, and the configuration of rotorhead 11 allows for gimballing of yoke 15 about flapping axes 26 relativeto trunnion carrier 21 and mast 19 while providing a constant path fortorque from mast 19 to yoke 15., An upper hub spring 27 and a lower hubspring 29 are used to allow for gimballing and provide a centering forcefor rotor head 11. In the embodiment shown in the FIGS. 1 through 3,coupling 13 comprises four pad-bearing assemblies 25. Though only onepad-bearing assembly 25 is described below, the description applies toeach one of assemblies 25.

Each pad-bearing assembly 25 comprises a rigid central member 31 andelastomeric pad bearings 33 affixed to central member 31 on opposingsides of central member 31. Central member 31 has a central bore 35having an axis that is collinear with the corresponding flapping axis26. Bore 35 is configured for installation of a spherical bearing 37therein, spherical bearing 37 preferably being a laminated sphericalbearing, though other types of bearings may be used. When sphericalbearing 37 is installed in bore 25, an outer spherical surface 39 ofbearing 37 is affixed to the inner wall of bore 35. Bearing 37 has acentral bore 41 configured for installation of an inner member 43therein. When inner member 43 is installed in bore 41, an outerspherical surface 45 is affixed to the inner wall of bore 41. Innermember 43 has a central bore 47 (shown in broken lines) configured toreceive trunnion 23 and terminating at the outer end in an alignmentpattern 49. Alignment pattern 49 is formed in inner member 43 forcooperative engagement with a corresponding alignment pattern 51 on theouter end of trunnion 23 for biasing inner member 43 toward a selectedangular orientation relative to trunnion 23. This allows central member31 to rotate a limited amount about trunnion 23 through elastic sheardeformation of the elastomeric layers of spherical bearing 37.

Each pad-bearing assembly 25 has two pad bearings 33, and pad bearing 33is shown in detail in FIGS. 4 and 5. Each of the pad bearings 33 in apad-bearing assembly 25 is a mirror image of the other bearing 33 in theassembly 25. One pad bearing 33 is shown in FIGS. 4 and 5 and describedbelow, though the description also applies to all pad bearings 33 incoupling 13. FIG. 4 is a side view of pad bearing 33 and shows that padbearing 33 is formed to curve outward with a large radius of curvature,the foci lying on the corresponding flapping axis 26 when pad bearing 33is installed in coupling 13. FIG. 5 is a cross-sectional view as viewedfrom the top and taken along the line V-V in FIG. 4. Pad bearing 33 ispreferably a laminated bearing, comprising alternating rigid layers 53and elastomeric layers 55 in a stacked arrangement, the outermost rigidlayers forming an inner surface 57 and an outer surface 59. As shown inFIG. 5, pad bearing 33 is provided with a chevron-shaped, or V-shaped,cross-section for providing greater stability in pad bearing 33 aslayers 53, 55 of pad bearing 33 are moved relative to each other throughelastic shear deformation of elastomeric layers 55.

Referring again to FIGS. 1 through 3, inner surface 57 of each padbearing 33 is adhered or otherwise affixed to one of a pair of bearingmount surfaces 61 of central member 31. Each bearing mount surface 61has a chevron-shaped cross-section for engaging that of inner surface57. A thrust plate 63 is adhered or otherwise affixed to each padbearing 33, an inner surface 65 of thrust plate 63 being affixed toouter surface 59 of pad bearing 33. To mount pad-bearing assemblieswithin coupling 13, an outer surface 67 of each thrust plate 63 isadhered or otherwise affixed to a bearing mount 69.

Each bearing mount 69 is a rigid body and has a pair of planar,generally vertical bearing mount surfaces 71 that are formed to begenerally perpendicular to each other. Bearing mount surfaces 71 ofadjacent bearing supports 69 face each other for creating mountinglocations for pad-bearing assemblies 25. Each bearing mount 69 has avertical pin 73 extending from the upper end of mount 69 and a verticalpin 75 extending from the lower end of mount 69. Bearing mounts 69 areattached to upper hub spring 27 by pins 73 extending through holes 77,which are located on the periphery of upper hub spring 27. Each pin 73is retained in hole 77 by cap 79. Bearing mounts 69 are attached to yoke15 by pins 75 extending through holes 81 in yoke 15. Alternatively, avertical bore may be formed in each bearing mount 69, and a pin mayextend through and beyond the ends of bearing mount 69 to form pins 73,75.

Each pad bearing assembly 25 is installed between adjacent bearingmounts 69. To install bearing assembly 25, outer surface 67 of eachthrust plate 63 is fixedly adhered or otherwise affixed to an adjacentbearing mount surface 71 of bearing mount 69. This configuration allowsfor limited relative movement between central member 31 and bearingmounts 69 through elastic shear deformation of elastomeric layers 55 ofpad bearings 33. This, in turn, allows for gimballing of yoke 15relative to mast 19 and trunnions 23 while providing a path forcontinuous transfer of torque from mast 19 to yoke 15.

When installed, each trunnion 23 engages inner member 43 of bearing 37,with each trunnion 23 engaging alignment pattern 49 formed in innermember 43 with a corresponding alignment pattern 51 on the outer end oftrunnion 23. Each thrust plate 63 is affixed to a corresponding bearingmount surface 71 of each of a pair of bearing mounts 69, allowing torqueto be transferred from trunnions 23 through inner members 43 andspherical bearings 37 into central members 31, and then through padbearings 33 and thrust plates 63 into bearing mounts 69. The torque isthen transferred from bearing mounts 69 into yoke 15 through pins 75 forrotating yoke 15 and attached rotor blades.

FIGS. 6 and 7 illustrate a rotor head 111 incorporating an alternativeembodiment of a torque coupling 113 of the present invention. FIG. 7shows coupling 113 as partially exploded. Rotor head 111 has aconfiguration similar to that of rotor head 11, described above, andsimilar numbers are used to identify similar components. Rotor head 111comprises coupling 113 and a yoke 115 mounted to coupling 113 forrotation with coupling 113. Yoke 115 is configured to allow for rotorblades (not shown) to be attached to outer portions 117 of yoke 115.Rotor head 111 is shown assembled onto a rotor mast 119 for rotation ofrotor head 111 when mast 119 is rotated about axis 120.

Torque is transferred though a splined connection from mast 119 intotrunnion carrier 121, which is preferably a unitary piece having fourtrunnions 123 extending radially from trunnion carrier 121. Torque istransferred from each trunnion 123 into one of a plurality ofpad-bearing assemblies 125. The embodiment shown in FIGS. 6 and 7comprises four pad-bearing assemblies 125, though rotor head 111 can beconfigured to have more or fewer assemblies 125. Each pair of opposingtrunnions 123 forms a flapping axis 126, and the configuration of rotorhead 111 allows for gimballing of yoke 115 about flapping axes 126relative to trunnion carrier 121 and mast 119 while providing a constantpath for torque from mast 119 to yoke 115. An upper hub spring 127 and alower hub spring 129 are used to allow for gimballing and provide acentering force for rotor head 111. In the embodiment shown in the FIGS.6 and 7, coupling 113 comprises four pad-bearing assemblies 125. Thoughonly one pad-bearing assembly 125 is described below, the descriptionapplies to each one of assemblies 125.

Each pad-bearing assembly 125 comprises a rigid central member 131 andelastomeric pad bearings 133 affixed to central member 131 on opposingsides of central member 131. Pad bearings 133 are preferably laminatedbearings, with alternating rigid and elastomeric layers in a stackedarrangement. The layers of pad bearings 133 are generally planar andlack the chevron-shaped cross-section of pad bearings 33. Central member131 has a central bore 135 having an axis that is collinear with thecorresponding flapping axis 126. Bore 135 is configured for installationof a spherical bearing 137 therein, spherical bearing 137 preferablybeing a laminated spherical bearing, though other types of bearings maybe used. When spherical bearing 137 is installed in bore 125, an outerspherical surface 139 of bearing 137 is affixed to the inner wall ofbore 135. Bearing 137 has a central bore 141 configured for installationof an inner member 143 therein. When inner member 143 is installed inbore 141, an outer spherical surface 145 is affixed to the inner wall ofbore 141. Inner member 143 has a central bore 147 (shown in brokenlines) configured to receive trunnion 123 and terminating at the outerend in an alignment pattern 149. Alignment pattern 149 is formed ininner member 143 for cooperative engagement with a correspondingalignment pattern 151 on the outer end of trunnion 123 for biasing innermember 143 toward a selected angular orientation relative to trunnion123. This allows central member 131 to rotate a limited amount abouttrunnion 123 through elastic shear deformation of the elastomeric layersof spherical bearing 137.

Inner surface 157 of each pad bearing 133 is adhered or otherwiseaffixed to one of a pair of bearing mount surfaces 61 of central member131. A thrust plate 163 is adhered or otherwise affixed to each padbearing 133, an inner surface 165 of thrust plate 163 being affixed toouter surface 159 of pad bearing 133. To mount pad-bearing assemblieswithin coupling 113, an outer surface 167 of each thrust plate 163 isadhered or otherwise affixed to a bearing mount 169.

Each bearing mount 169 is a rigid body and has a pair of planar,generally vertical bearing mount surfaces 171 that are formed to begenerally perpendicular to each other. Bearing mount surfaces 171 ofadjacent bearing supports 169 face each other for creating mountinglocations for pad-bearing assemblies 125. Each bearing mount 169 has avertical pin 173 extending from the upper end of mount 169 and avertical pin 175 extending from the lower end of mount 169. Bearingmounts 169 are attached to upper hub spring 127 by pins 173 extendingthrough holes 177, which are located on the periphery of upper hubspring 127. Each pin 173 is retained in hole 177 by cap 179. Bearingmounts 169 are attached to yoke 115 by pins 175 extending through holes181 in yoke 115. Alternatively, a vertical bore may be formed in eachbearing mount 169, and a pin may extend through and beyond the ends ofbearing mount 169 to form pins 173, 175.

Each pad bearing assembly 125 is installed between adjacent bearingmounts 169. To install bearing assembly 125, outer surface 167 of eachthrust plate 163 is fixedly adhered or otherwise affixed to an adjacentbearing mount surface 171 of bearing mount 169. This configurationallows for limited relative movement between central member 131 andbearing mounts 169 through elastic shear deformation of elastomericlayers of pad bearings 133. This, in turn, allows for gimballing of yoke115 relative to mast 119 and trunnions 123 while providing a path forcontinuous transfer of torque from mast 119 to yoke 115.

When installed, each trunnion 123 engages inner member 143 of bearing137, with each trunnion 123 engaging alignment pattern 149 formed ininner member 143 with a corresponding alignment pattern 151 on the outerend of trunnion 123. Each thrust plate 163 is affixed to a correspondingbearing mount surface 171 of each of a pair of bearing mounts 169,allowing torque to be transferred from trunnions 123 through innermembers 143 and spherical bearings 137 into central members 131, andthen through pad bearings 133 and thrust plates 163 into bearing mounts169. The torque is then transferred from bearing mounts 169 into yoke115 through pins 175 for rotating yoke 115 and attached rotor blades.

The present invention provides for several advantages, including: (1)reduced size; (2) reduced weight; and (3) the ability to transfer hightorque.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription.

1. A torque coupling for a rotor head of a rotary-wing aircraft, thetorque coupling being configured for rotation with a mast and forcausing rotation of an attached yoke; the coupling comprising: aplurality of trunnions adapted for rotation with the mast about an axisof rotation, the trunnions extending generally radially relative to theaxis; a plurality of pad-bearing assemblies, each assembly comprising: acentral member pivotally coupled to one of the trunnions; and aplurality of laminated pad bearings affixed to opposing sides of thecentral member, each pad bearing comprising a plurality of rigid layersand a plurality of elastomeric layers in a stacked configuration, atleast one elastomeric layer being located between adjacent rigid layers;and a bearing mount affixed to each pad bearing and adapted to beconnected to a yoke; wherein the pad-bearings allow for relative motionbetween each central member and the associated bearing mounts throughelastic shear deformation of the elastomeric layers of the pad bearings,which allows for relative motion between an attached yoke and the mast.2. The torque coupling according to claim 1, further comprising: alaminated spherical bearing located in each central member; wherein eachtrunnion is pivotally coupled to an associated central member with thespherical bearing.
 3. The torque coupling according to claim 1, whereineach pad bearing is a flat pad bearing.
 4. The torque coupling accordingto claim 1, wherein each pad bearing is a curved pad bearing having afocus spaced from the pad bearing.
 5. The torque coupling according toclaim 1, wherein the pad bearings of each pad-bearing assembly have focithat define a line that intersects the axis of rotation.
 6. The torquecoupling according to claim 1, wherein the torque coupling comprises aplurality of bearing mounts, wherein each bearing mount has at least twomounting surfaces that are generally vertical and generallyperpendicular to each other, and wherein at least one pad-bearingassembly is attached to an opposing pair of bearing mounts.
 7. A torquecoupling for a rotor head of a rotary-wing aircraft, the torque couplingbeing configured for rotation with a mast and for causing rotation of anattached yoke; the coupling comprising: a plurality of trunnions adaptedfor rotation with the mast about an axis of rotation, the trunnionsextending generally radially relative to the axis; a plurality ofpad-bearing assemblies, each assembly comprising: a central memberpivotally coupled to one of the trunnions; and at least one laminatedpad bearing affixed to each of opposing sides of the central member,each pad bearing comprising a plurality of rigid layers and a pluralityof elastomeric layers in a stacked configuration; and an opposing pairof bearing mounts, each of the opposing pair of bearing mounts having atleast two curved mounting surfaces, at least one pad-bearing assemblybeing attached to the opposing pair of bearing mounts, wherein thepad-bearings allow for relative motion between each central member and the associated bearing mounts through elastic shear deformation of theelastomeric layers of the pad bearings and rotation of each centralmember relative to the associated trunnion, which allows for relativemotion between an attached yoke and the mast.
 8. The torque couplingaccording to claim 7, further comprising: a laminated spherical bearinglocated in each central member; wherein each trunnion is pivotallycoupled to an associated central member With the spherical bearing. 9.The torque coupling according to claim. 7, wherein each pad bearing hasa v-shaped cross-section.
 10. The torque coupling according to claim 7,wherein each pad bearing is a curved pad bearing having a focus spacedfrom the pad bearing.
 11. The torque coupling according to claim 7,wherein the pad bearings of each pad-bearing assembly have foci thatdefine a line that intersects the axis of rotation.